In general, inverted F-type antennas have excellent characteristics as internal antennas of small, thin radio terminals typified by portable telephones.
FIG. 21 is a perspective view showing the typical construction of a conventional inverted F-type antenna.
Referring to FIG. 21, in the inverted F-type antenna 210, an emission conductor 212 is arranged opposite a ground conductor 211, the emission conductor 212 being connected to the ground conductor 2112 through a ground conductor 213.
Also, a feeding point 212a is provided on emission conductor 212, and power is supplied to the feeding point 212a by means of a coaxial feeding line 214 from power feeding source 215 through a hole 211 a provided in ground conductor 211.
As is known, assuming that the length of emission conductor 212 is L1 as shown in FIG. 21, the inverted F-type antenna 210 resonates with the frequency at which the length L1 is about .lambda./4 (where .lambda. is the wavelength).
However, with radio terminals of this type, it is demanded that the inverted F-type antenna should be capable of receiving two or more different frequency bands together in order for example to be capable of being employed in two or more systems.
The constructions shown in FIG. 22 or FIG. 23 are known as conventional constructions whereby it is made possible to receive two or more different frequency bands together, using an inverted F-type antenna.
FIG. 22 is a perspective view showing a conventional multifrequency inverted F-type antenna that is capable of receiving two or more different frequency bands together.
Referring to FIG. 22, in the multifrequency inverted F-type antenna 220, two emission conductors 222-1 and 222-2 of different size are arranged in parallel with respect to ground conductor 221; these two emission conductors 222-1 and 222-2 are connected to ground conductor 221 through respective ground conductors 223-1 and 223-2; power is supplied to feeding point 222-1 a on emission conductor 222-1 from power feeding source 225-1 by coaxial feeding line 224-1 and power is supplied to feeding point 222-2a on emission conductor 222-2 from power feeding source 225-2 by coaxial feeding line 224-2.
Specifically, in the multifrequency inverted F-type antenna 220 shown in FIG. 22, an arrangement is adopted whereby two single-frequency inverted F-type antennas that resonate in respectively different frequency bands are arranged adjacently; as a result, there is the problem that the installation area becomes large in order to permit the arrangement of these two single-frequency inverted F-type antennas.
FIG. 23 is a perspective view showing another conventional multifrequency inverted F-type antenna which is capable of receiving two or more different frequency bands at once.
Referring to FIG. 23, in the multifrequency inverted F-type antenna 230, two emission conductors 232-1 and 232-2 of different size are arranged in stacked fashion relative to ground conductor 231, these two emission conductors 232-1 and 232-2 being connected to ground conductor 231 through respective ground conductors 233-1, 233-2; feeding point 232-1 a on emission conductor 232-1 is supplied with power from power feeding source 235-1 by coaxial feeding line 234-1, while feeding point 232-2a on emission conductor 232-2 is supplied with power from power feeding source 235-2 by means of coaxial feeding line 234-2.
Specifically, with the construction shown in FIG. 23, two single-frequency inverted F-type antennas that resonate in respectively different frequency bands are arranged in stacked fashion; as a result, there is the problem that the installation volume becomes large owing to the increased height of the installation region in order to provide for the stacked arrangement of these two single-frequency inverted F-type antennas.
Thus, there was the problem that, with a conventional multifrequency inverted F-type antenna arranged to be capable of receiving simultaneously two or more different frequency bands, there was the problem that the installation area or installation volume became larger than that of a conventional single-frequency inverted F-type antenna, thereby presenting an obstacle to reducing the size and thickness of a radio terminal accommodating such a multifrequency inverted F-type antenna.